1. Field of the Invention
The present invention relates to a tuner card for use with a notebook-size personal computer as well as to a tuner incorporated in the tuner card.
2. Description of the Related Art
Recent years have seen the development of a thin-sized television signal receiving unit mounted on a card-type printed-circuit board (called a tuner card) for use with a personal computer Equipped with the tuner card, the personal computer may have television pictures displayed on its display unit.
A conventional tuner card will now be outlined with reference to FIGS. 7 and 8. At one end of a rectangular printed-circuit board 41 is formed a connector part 41a for connection with a personal computer (not shown). At another end of the printed-circuit board 41 in the opposite direction of the connector part 41a is a tuner 42 mounted along the end. The tuner 42 comprises a metal case incorporating a tuner board (not shown) carrying necessary circuitry. On one edge of the metal case is a connector 42a. The tuner 42 is mounted on the print-circuit board 41 so that the connector 42a is oriented in the opposite direction of the connector part 41a. The connector 42 is fed with television signals from an external antenna (not shown).
A region 41b between the connector part 41a and the tuner 42 on the printed-circuit board 41 comprises electronic parts (not shown) constituting digital circuits. These circuits serve as an interface that allows video and other signals from the tuner 42 to be admitted to the personal computer.
The tuner card is inserted into the personal computer through a slot (not shown) on one side of the PC body, so that the connector part 41a is plugged into a connector (not shown) inside the PC. In this state, the region 41b carrying the electronic parts making up the digital circuits is located within the slot while the tuner 42 extends laterally outside the PC. The height of the region 41b on the printed-circuit board 41 is about 5 mm so that the card fits snugly into the PC slot.
An antenna, not shown, is connected to the connector 42a on the side of the tuner 42. Through the antenna and the connector 42a, television signals are input to the tuner 42.
FIG. 8 is a schematic block diagram of the tuner 42. As illustrated, an input terminal 51 connected to the connector 42a admits television signals on the VHF and UHF bands The television signals are split by a branching circuit 52 into the signals on the VHF band and those on the UHF band The branched signals are input respectively to a VHF tuner unit 53 and a UHF tuner unit 54 wherein the television signal of a desired channel is selected and converted in frequency to an intermediate frequency signal. The intermediate frequency signal is amplified and accorded a selective specificity by an intermediate frequency circuit 55. From the circuit 55, the signal is sent to a demodulator 56 which derives video signal V and audio signal A from the received signal.
The tuner 42 has a band switching voltage generating circuit 57 for selecting a reception band to which the selected television signal belongs. A channel selecting signal S either from a television set or from the personal computer is admitted to the band switching voltage generating circuit 57. There are three kinds of reception bands: the UHF band, the VHF high-band, and the VHF low-band. Where a UHF band television signal is to be received, the band switching voltage generating circuit 57 outputs a UHF band switching voltage UB through its output terminal 57a to the UHF tuner unit 54. Likewise, upon reception of a VHF high-band television signal, the circuit 57 outputs a high-band switching voltage HB through its output terminal 57b to the VHF tuner unit 53; for receiving a VHF low-band television signal, the band switching voltage generating circuit 57 outputs a low-band switching voltage LB through its output terminal 57c to the VHF tuner unit 53.
There are some disadvantages involved in the use of the conventional tuner above constituting a tuner card for use with the notebook-size personal computer. The notebook computer is originally intended for portable and mobile use free from constraints specific to the location. If an antenna is available at the site of use or if an antenna cable connected to an exterior antenna is led into the site, that antenna or antenna cable may be connected to the connector 42a of the tuner 42. In many cases, however, neither antenna nor antenna cable is available where the notebook computer is desired to be operated. This poses limits to where the notebook computer may be used if television signals need to be admitted to the computer.